This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Severe combined immune deficiency (SCID) represents the most extreme primary immune deficiency with a life-span of less than 1-2 years in most children without therapy due to overwhelming infections. Adenosine deaminase (ADA)-deficient SCID, which accounts for ~20% of human cases of SCID, is unique among the different genetic types of SCID in that it results from the absence of an enzyme (ADA). Although ADA is expressed in all tissues, the absence of ADA enzyme is most critical to the survival of lymphocytes and, in the absence of ADA, toxic metabolites accumulate in lymphocytes and causes severe metabolic derangements and cell death. The objective of these studies is to assess vector pharmacokinetics, dosimetry, and biodistribution in infant monkeys as pre-clinical studies prior to testing in human infants. These studies are essential to translate this approach to human ADA-deficient SCID pediatric patients.